This invention relates to a composition for thermistor, and more particularly to a composition for high temperature thermistors.
The conventional thermistors have been used for temperature measurement usually in the range of from room temperature to about 300.degree.C. Such kind of thermistor is of a composition comprising cobalt oxide, manganese oxide, nickel oxide and/or iron oxide.
Recently, a high temperature thermistor which can be operable at a high temperature range up to about 1000.degree.C has been developed. For example, it was disclosed in Japanese Pat. Publication S41-15855/1966 that the thermistors, which consists of the solid solution of SnO.sub.2 -TiO.sub.2 system as the principal component and additive of at least one oxide selected from the group consisting of Sb.sub.2 O.sub.3 and Ta.sub.2 O.sub.3 in the amount of less than 5% by mole, were able to be used in a high temperature up to 1000.degree.C. It was also disclosed in Rev. of Scientific Inst., 40 pp. 544-549 (1969) that the thermistors consisting of ZrO.sub.2 as the principal component and additive of Y.sub.2 O.sub.3 were able to be operable in a high temperature to about 1000.degree.C. Furthermore, it was disclosed in U.S. Pat. No. 3,598,764 (1971) that the thermistors consisting of CeO.sub.2 as the principal component and additive of ZrO.sub.2 in the amount of 2 to 15% by weight were able to be used in a high temperature up to 1000.degree.C.
However, these conventional materials for a high temperature thermistor have inferior and time-dependent characteristics. Particularly, they display unstability in usage on a high temperature under an application of a d.c. voltage.
Recently, a high temperature thermistor which can be used in a working temperature above 300.degree.C has been intensively required. For example, it is desired to be used for a temperature controller, which has the working temperature range of 600.degree.C to 1000.degree.C, of a thermal reactor of a motor car in which an exhausting gas from an engine is reburnt. In such a case, the high temperature thermistors must be used under an application of d.c. voltage, because an electric power source in a motorcar is a d.c. electrical battery.